Fast moisture curing and UV-moisture dual curing compositions

ABSTRACT

The invention provides fast moisture and photo/moisture curing silicone compositions and methods for the preparation thereof. More particularly, the compositions provided are prepared from silanol and silane cappers; the cappers have an α-carbon bonded to the silicon atom allowing for a favorable hypervalent silicon transition state when reacting the silane and silanol. This favorable transition state enables both a fast endcapping reaction and contributes to the fast moisture curing properties of the inventive compositions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of International PatentAppl.Ser. No. PCT/US2003/32537 filed Oct. 15, 2003, which claims thebenefit of an earlier filing date under 35 U.S.C. § 120 to U.S.Provisional Appl. No. 60/470,705 filed Oct. 23, 2002.

FIELD OF THE INVENTION

The invention provides fast moisture and photo/moisture curing siliconecompositions and methods for the preparation thereof. More particularly,the compositions provided are prepared from silanol and silane cappers;the cappers have an α-carbon bonded to the silicon atom allowing for afavorable hypervalent silicon transition state when reacting the silaneand silanol. This favorable transition state enables both a fastendcapping reaction and contributes to the fast moisture curingproperties of the inventive compositions.

BRIEF DESCRIPTION OF RELATED TECHNOLOGY

The quest for fast curing silicone compositions that are both simple andeconomical to prepare as well as useful in a variety of industrialapplications has lead to many developments for such compositions inrecent years (e.g. U.S. Pat. Nos. 4,528,081; 4,699,802; 4,675,346assigned to Henkel Loctite Corporation and U.S. Pat. Nos. 5,405,888;5,409,963; 5,489,622; 5,384,340, 5,340,847 assigned to Three Bond Co.Ltd.). Notably, Chu (Chu, H. K., in Silicones and Silicone-ModifiedMaterials, ed. Clarson, et al., American Chemical Society, WashingtonD.C., 2000, pp 170-179) has reported that silanol terminatedpolydimethylsiloxane (PDMS) can be readily endcapped withacryloxymethyldimethylacryloxysilane by simply mixing this silane withsilanol terminated PDMS. The reaction is generally complete withinseconds after mixing as evidenced by the transformation of the clearsilanol fluid into a cloudy mixture due to the low solubility of theliberated acrylic acid in silicone. Removal of acrylic acid by vacuumstripping, if needed, yields the clear acrylate endcappedpolydimethylsiloxane. Addition of a photoinitiator, fillers and othertypes of additives common to RTV silicones results in photo (i.e.ultraviolet or “UV”) curable silicones.

The ease of this reaction was reported by Chu as being unexpected. Incondensation reactions of acetoxysilanes with silanol, the reactivity ofthese silanes has been reported to be directly proportional to thenumber of acetoxy groups attached to silicon, presumably due to theelectron withdrawing capability of the acetoxy groups that renders thesilanes with more acetoxy groups more anenable to nucleophilicsubstitution. Thus, condensation with silanol takes placeinstantaneously with tetra-or triacetoxysilanes, but is orders ofmagnitude slower for diacetoxy-or monacetoxysilanes. Thus,acryloxymethyldimethylacryloxysilane, with only one acryloxy groupdirectly attached to silicon, was reportedly expected to likewise reactwith silanol very slowly.

A reported explanation for the ease of this endcapping reaction wasattributed to a hypervalent transition state (see Chu, above). Severalsimilar silanes with a carbonyl group γ- to silicon have been shown topossess pentacoordinate silicon structures with an intramolecularcoordinate Si←O═C bond. High reactivities of many such hypervalentsilicon compounds have been observed and are attributed to thehypervalency of these silanes (see Chu, above). Althoughacryloxymethyldimethylacryloxysilane has been reported to betetracoordinate, rather than exhibiting pentacoordinate hypervalency,the high reactivity between this silane and silanol has been attributedto the anchimeric assistance of the acryloxymethyl group on the leavingacryloxy group during endcapping of the silanol. A hexacoordinatehypervalent transition state (resulting from the intramolecularcoordinate from both the Si←O═C bond and the O bond from the silanol)has been proposed to be responsible for the ease of the reaction (seeChu, page 178) and the proposed structure below:

Although as described above, photocurable silicon compositions have beendeveloped using cappers such as acryloxymethyldimethylacryloxysilanethat allow for a favorable silicon transition state resulting in fastendcapping reactions, compositions derived from such cappers that willresult in moisture or dual (UV/moisture) curing silicone compositionsare needed.

Furthermore, there is a need for faster curing moisture curablecompositions. As is well known in the art, many moisture-curing siliconesystems provide good physical properties and performance when fullycured, but they suffer from the disadvantage of slow cure. Bauer et al(“NCO-Silane Terminated Copolymers with Tunable Curing Rates”, Munich,2001, 1^(st) European Silicon Days) have reported, however, thatpolymers derived from isocyanatomethylalkoxysilanes (i.e. those silaneshaving an α-carbon bonded to the silicon atom) and aminoalkyl/siliconesresult in an extremely enhanced curing rate, putatively due to thehypervalent transition state that occurs during curing (i.e.cross-linking of reactive silicones) when exposed to ambient conditions.However the isocyanatosilanes used to create these polymers may be ofconcern due to the undesirable toxicological effects of isocyanates ingeneral.

Hence, there is a need in the art for photo/moisture curable andmoisture curable compositions having fast moisture curing propertiesthat can be prepared by simple, safe and economical methods and alsoallow for fast endcapping reactions

SUMMARY OF THE INVENTION

The invention provides compositions capable of fast moisture cure. Thecompositions, which include both hydrolyzable functional silanes andsilanols may be exclusively moisture curing or dual (photo/moisture)curing. The silanes contain a single carbon linkage between the siliconatom and, for example, an acetyl or methacryloyl group (see structure Ibelow). This linkage provides for the formation of a favorablehypervalent silicon transition state, allowing fast nucleophilicsubstitution on silicon during endcapping and curing reactions.

More particularly, the invention provides a composition including:

-   -   a) a compound having the structural formula:

-   -   wherein R is a C₁₋₂₀ alkyl which may be substituted or        unsubstituted or an unsaturated free radical-curing group;    -   R¹ is hydrogen or a C₁₋₆ hydrocarbon radical; R² is a        hydrolyzable group; X is oxygen or

R³ is H or C₁₋₁₂ hydrocarbyl group; and

-   -   b) a polymer having the structure formula:

-   -   wherein A is a backbone selected from the group consisting of        organic and siloxane backbones, and R^(e) is CH₃ or H.

Further provided is a curable composition having the reaction product of

-   -   a) a compound having the structural formula:

wherein R is a C₁₋₂₀ alkyl which may be substituted or unsubstituted oran unsaturated free radical-curing group;

-   -   R¹ is hydrogen or a C₁₋₆ hydrocarbon radical; R² is a        hydrolyzable group; X is oxygen or

R³ is H or C₁₋₁₂ hydrocarbyl group; and

-   -   b) a polymer having the structure formula:

-   -   wherein A is a backbone selected from the group consisting of        organic and siloxane backbones, and R^(e) is CH₃ or H.

Furthermore, in another aspect of the invention there is provided amethod of preparing a curable composition including the step ofcombining:

-   -   a) a compound having the structural formula:

wherein R is a C₁₋₂₀ alkyl which may be substituted or unsubstituted oran unsaturated free radical-curing group;

-   -   R¹ is hydrogen or a C₁₋₆ hydrocarbon radical; R² is a        hydrolyzable group; X is oxygen,

R³ is H or C₁₋₁₂ hydrocarbyl group; and

-   -   b) a polymer having the structure formula:

-   -   wherein A is a backbone selected from the group consisting of        organic and siloxane backbones, and R^(e) is CH₃ or H.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the invention, a curable composition is provided havinga silane capper compound of the formula:

wherein R is a C₁₋₂₀ alkyl which may be substituted or unsubstituted oran unsaturated free radical-curing group;

-   -   R¹ is hydrogen or a C₁₋₆ hydrocarbon radical; R² is a        hydrolyzable group; X is oxygen or

R³ is H or C₁₋₁₂ hydrocarbyl group; and

-   -   a silanol-terminated polymer having the structure:

-   -   wherein A is a backbone selected from the group consisting of        organic and siloxane backbones, and R^(e) is CH₃ or H.

In a desired embodiment, R² is selected from the group consisting of

-   -   wherein R′, R″, R″′ and R″″ is H or a monovalent substituted or        unsubstituted C₁₋₆ hyd1rocarbon radical, and R⁴ is a C₁₋₂ alkyl        group.

In a particularly desired embodiment, R² is selected from the groupconsisting of

-   -   wherein R⁴ is a C₁₋₂ alkyl group.

In a particularly desired embodiment, R² is an alkoxy group having theformulaR⁴O—

-   -   wherein R⁴ is a C₁₋₂alkyl group.

In another desired embodiment, R is a C₁₋₂₀ alkyl or C₂₋₂₀ alkenyleither of which may be substituted or unsubstituted.

Desirably, both moisture and photo curable groups are present on thesilane capper of the invention. In this embodiment, the compositionincludes a silane capper wherein R includes an unsaturated freeradical-curing group (i.e. a C₂₋₂₀ alkenyl which may be substituted orunsubstituted), capable of undergoing free radical cure, such as UVcure, and R¹, R², X, and R³ are as described above and structuralformula II is as described above.

In another desired aspect of the invention, a moisture curablecomposition is provided wherein the silane capper exclusively includesmoisture curable groups. In this embodiment, the composition includesstructural formula I wherein R is a C₁₋₂₀ alkyl which may be substitutedor unsubstituted, R¹, R², X, and R³ are as described above, andstructural formula II is as described above.

Regardless of whether the final composition is curable by UV, moistureor both, the most desirable silane capper has the general formula III

-   -   wherein R, R¹, R² and R⁴ are as described above.

Among capper compounds of the general formula III set out broadlyhereinabove, a preferred class of such compounds includes those in whichthe alkoxyfunctional silane contains a carboxyl group. Therefore, X isdesirably O. Thus a preferred class of compounds are of the formula:

-   -   wherein R, R¹ and R⁴ are as defined above.

In a particularly desired preferred embodiment, a photo/moisture curablecomposition is provided which includes a polymer according to structuralformula II and an alkoxysilane according to structural formula IVwherein R is

-   -   and R⁵, R⁶ and R⁷ are independently selected from hydrogen,        halogen and organo radicals, and R¹ and R⁴ are as described        above.

In a particularly desired embodiment, the structure of the silane capperused in the photo/moisture curing composition is an alkoxysilane offormula IV wherein R is structural formula V and R⁵ and R⁶ are H and R⁷is CH₃. Hence, a particularly desired embodiment of the silane capper isthat of structural formula VI below:

In yet, another desirable embodiment, the structure of the capper usedin the curing composition of the invention is an alkoxysilane ofstructural formula IV wherein R is a methyl group and R¹ and R⁴ are asdescribed above. Thus, in this embodiment the desired structure is ofstructural formula VII below.

The synthesis of the silane cappers described above may be prepared byany desirable method known in the art. For example, the synthesis of anacryloxy-functional alkoxysilane such as that of structural formulas VImay prepared by using the following reaction step:

-   -   (a) reacting (i) a (meth)acrylic acid compound of the formula:

-   -   wherein R⁵, R⁶ and R⁷ are independently selected from hydrogen,        halo and organo radicals, with (ii) a chlorosilane compound of        the formula:

-   -   wherein R⁴ is as described above.

In another embodiment, the proton in structural formula VII may bereplaced with Na⁺ or K⁺ and reacted with structural formula IX.

In carrying out the reaction of the (meth)acrylic acid compounds withthe chlorosilane compounds, it is generally advantageous to use a basesuch as triethylamine under refluxing xylene or dimethylformamide tofunction as a hydrogen chloride acceptor, thereby removing the hydrogenchloride formed in the reaction. In some instances, it may be feasibleto remove the hydrogen chloride by-product by sparging the reactionmixture with nitrogen, whereby the passage of nitrogen throughout themixture removes the hydrogen chloride. Additionally, acrylatepolymerization inhibitor such as hydroquinone (HQ) may also optionallybe added to the mixture.

In an alternative embodiment, where X in structural formula I is

-   -   wherein R³ is H or a C₁₋₁₂ hydrocarbon radical, structural        formula I may be formed by reacting amino methyltrialkoxysilane        with methacryl chloride.

The reaction may be carried out at any suitable temperature; generally,temperatures on the order of from about 25° C. to about 150° C. areusefully employed and preferably from about 100° C. to 140°, mostpreferably at about 120° C. The time required to carry out the reactionmay be readily determined for a given reaction system by simpleanalytical tests without undue experimentation, and the reaction timemay be varied as necessary or desirable in a given application. By wayof example, the reaction may be carried out in approximately 2-3 hours.After the reaction has been carried out, the reaction mixture mayoptionally be subjected to vacuum stripping or other suitable treatmentfor the removal of residual acrylic acid from the reaction mixture tothe extent desired.

Similarly, an alkoxysilane capper of the invention containing an acetoxyfunctional group may be prepared by reacting acetic acid with structureIX to yield a reaction product such as that of structure VII where R¹ isH.

The silanol-terminated polymer of structural formula II can be virtuallyany useful silanol-terminated material. The silanol-terminated polymeras described above has the general formula

wherein A represents a polymer or copolymer backbone. The backbone canbe any number of combinations of polyurethane, silicone, polyamide,polyether and the like. Desirably, A is an organic or a siloxanebackbone. More desirably, A is a siloxane.

An example of one such silanol-terminated polymer ispolydimethylsiloxane having the formula:

The number of repeating units will determine the molecular weight andhence the viscosity of this starting material. Thus, n can be, forexample, an integer which, for example, can be from about 1 to about1,200, desirably from about 10 to about 1,000. The viscosity of thesematerials is not critical and can easily be chosen to fit a particularproduct application, particularly because the hydrolyzable terminatedend product of this reaction will have substantially the same viscosityas the silanol-terminated reactant. Viscosities of thesesilanol-terminated polymer backbone can range from about 1 cps to about150,000 cps (Brookfield, 25° C.). Desirably, the silanol-terminatedpolymer backbone used in the present invention is from about 50 to about150,000 cps. Useful silanol terminated polymers include those from about50 cps silanol-terminated polydimethylsiloxane, to about 150,000 cpssilanol-terminated polydimethylsiloxane and combinations thereof.

The invention also provides a curable composition including the reactionproduct of a silane capper as described above with the polymer ofstructural formula II also as described above. The reaction of structureI and II, due to the carbon diradical linkage between the silicon in thecapper and the —X—CO—R group enables a favorable hypervalent silicontransition state during the capping reaction resulting in fastnucleophilic substitution on silicon.

Desirably, this reaction product cures in less than about 20 minutes.More desirably the reaction product cures in less than about 15 minutes.Even more desirably, the reaction product cures between about 3 minutesand about 14 minutes. Yet, even more desirably, the reaction productcures in about 5 minutes.

The determination that the reaction product is cured is measured byexamining the skin over time. As used herein, “skin over time” refers tothe time it takes for a spatula to no longer pick up liquid upon contactwith a reaction product.

The reaction of structure I and structure II of the present invention isdesirably performed in the presence of a catalyst. Desirable catalystsinclude organo-lithium reagents, which are represented by the formulaLiR¹² wherein the organo group R¹² is selected from the group consistingof C₁₋₁₈ alkyl, C₁₋₁₈ aryl, C₁₋₁₈ alkylaryl, C₁₋₁₈ arylalkyl, C₂₋₁₈alkenyl, C₂₋₁₈ alkynyl, amine-containing compounds, as well asorganosilicon-containing compounds. R¹² can have from 1 to 18 carbonatoms in the chain (C₁₋₁₈). These reagents provide enhanced processingand improved quality of product made therefrom

The organo-lithium catalyst is preferably an alkyl lithium such asmethyl, n-butyl, sec-butyl, t-butyl, n-hexyl, 2-ethylhexyl butyl andn-octyl butyl lithium. A particularly desirable catalyst isN-butyllithium in hexane (such as at 1.6 Molar concentration). Otheruseful catalysts include phenyl lithium, vinyl lithium, lithiumphenylacetylide, lithium (trimethylsilyl) acetylide, lithium silanolatesand lithium siloxanolates. The organo group can also be anamine-containing compound, such as dimethylamide, diethylamide,diisopropylamide or dicyclohexylamide, or a silicon-containing compound.(See, for example U.S. Pat. No. 5,300,608 (Chu); U.S. Pat. No. 5,663,269(Chu) and U.S. Pat. No. 6,140,444 (Chu)).

The organo-lithium reagents are used in catalytically effective amounts.Generally, the catalytically effective amount of an organo-lithiumcatalyst will vary with the specific catalyst and reactant materials,but about 1 to 1000 ppm based on the atomic weight of lithium areuseful. A more preferred range is 5-250 ppm. Removal of the residualorgano-lithium catalyst can be optionally accomplished throughfiltration.

Other catalysts useful in, but less desirable, in preparing the reactivesilicones include organometallic catalysts such as titanates and organotin catalysts known in the art.

The reactive silicone compositions of the invention may further includea curing system. A curing system includes but is not limited tocatalysts or other reagents which act to accelerate or otherwise promotethe curing of the composition of the invention.

When moisture curing is desirable, the catalysts which may be includedin the curing system of the invention include, but are not limited to,tin IV salts of carboxylic acids, such as dibutyltin dilaurate,organotitanium compounds such as tetrabutyl titanate, and partiallychelated derivatives of these salts with chelating agents such asacetoacetic acid esters and beta-diketones and amines. Desirably,tetraisopropyltitanate, dibutyltin dilaurate and tetramethylguandine atlevels of 0.05-0.5% are used.

Where photo curing is desirable, any known radical photoinitiators canbe included in the compositions of the invention. Photoinitiatorsenhance the rapidity of the curing process when the photocurablecompositions as a whole are exposed to electromagnetic radiation.Examples of suitable photointiators for use herein include, but are notlimited to, photoinitiators available commercially from Ciba SpecialtyChemicals, Tarrytown, N.Y. under the “IRGACURE” and “DAROCUR”tradenames, specifically “IRGACURE” 184 (1-hydroxycyclohexyl phenylketone), 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one), 369(2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone), 500(the combination of 1-hydroxy cyclohexyl phenyl ketone andbenzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone), 1700 (thecombination of bis(2,6-dimethoxybenzoyl-2,4,4-trimethyl pentyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one), and 819[bis(2,4,6-trimethyl benzoyl) phenyl phosphine oxide] and “DAROCUR” 1173(2-hydroxy-2-methyl-1-phenyl-1-propane) and 4265 (the combination of2,4,6-trimethylbenzoyldiphenylphosphine oxide and2-hydroxy-2-methyl-1-phenyl-propan-1-one); and the visible light [blue]photoinitiators, dl-camphorquinone and “IRGACURE” 784DC. Of course,combinations of these materials may also be employed herein.

Other photoinitiators useful herein include alkyl pyruvates, such asmethyl, ethyl, propyl, and butyl pyruvates, and aryl pyruvates, such asphenyl, benzyl, and appropriately substituted derivatives thereof.

Photoinitiators particularly well-suited for use herein includeultraviolet photoinitiators, such as 2,2-dimethoxy-2-phenyl acetophenone(e.g., “IRGACURE” 651), and 2-hydroxy-2-methyl-1-phenyl-1-propane (e.g.,“DAROCUR” 1173), diethoxyacetophenone, bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide (e.g., “IRGACURE” 819), and theultraviolet/visible photoinitiator combination ofbis(2,6-dimethoxybenzoyl-2,4,4-trimethylpentyl) phosphine oxide and2-hydroxy-2-methyl-1-phenyl-propan-1-one (e.g., “IRGACURE” 1700), aswell as the visible photoinitiatorbis(η⁵-2,4-cyclopentadien-1-yl)-bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium(e.g., “IRGACURE” 784DC).

The amount of photoinitiator used in the composition will typically bein the range of between about 0.1% and 5% of the composition. Dependingon the characteristics of the particular photoinitiator, however,amounts outside of this range may be employed without departing from theinvention so long as they perform the function of rapidly andefficiently initiating polymerization. In particular, higher percentagesmay be required if silicone bound photoinitiators are used with highequivalent weight per photoinitiating group.

The inventive compositions may also contain other additives so long asthey do not interfere with the curing mechanisms. The curable siliconecompositions of the present invention can be mixed with or include otherconventional additives such as viscosity modifiers such astrimethyl(silyl) terminated polydimethyl silicone, initiators,promoters, pigments, fillers, moisture scavengers and the like to form aone-part curable composition. Particularly useful fillers include fumedsilica, silane treated, calcium carbonate, calcium carbonate(hydrophobic) and combinations thereof. Desirable pigments additivesinclude carbon black. Moisture scavengers such as methyltrimethoxysilaneand vinyltrimethyloxysilane are useful.

Other particularly useful additives include hexamethyldisilazane,vinyltrimethoxysilane, aminopropyltriethoxysilane and combinationsthereof. Desirably, adhesion promoters include, but are not limited to,such as glycidoxypropyltrimethoxysilane, aminopropyltrimethoxysilane,methacryloxypropyltrimethoxy-silane,triallyl-S-tria-zine-2,3,6(1H.3H.5H)-trioneaminoethylaminopropyltrimethoxysilane and others known to those skilledin the art. Fillers such as silica, microballoon glass and the like areuseful for their conventional purposes.

The invention also provides a method of preparing a curable compositionincluding the steps of reacting a silane capper according to structuralformula I as described above with structural formula II. In this aspectof the invention, structural formula II may be devolitized under vacuumfor an appropriate time period as is known in the art, generally 1-2hours. The devolitization occurs at elevated temperatures, typicallybetween 80° C. to 150° C., more desirably between 100° C. and 110° C.After cooling the silanol of structural formula II to between about roomtemperature to about 90° C., and more preferably from about roomtemperature to 75° C., the silane capper is added to the silanol.

Desirably, a catalyst is used to increase the rate of capping. Desiredcatalysts include the organic lithium catalysts described above.Desirably, N-butyllithium in hexane (1.6 M) is used. Endcapping underthese conditions occurs immediately.

Although the silane capper of the invention and structural formula IImay be utilized in any suitable proportions relative to one anotherconsistent with the number of alcohol-reactive functional groups onstructure II, it generally is preferred to utilize relative amounts ofthe inventive capper and structure II providing up to about 1.5 or moreequivalents of silane for with the silane of structure II, and desirablythe equivalents ratio of silane to alcohol-functionality is from about1.0 to 1.2.

The method also provides a curing system as described above. Desiredcatalyst for use in moisture curing include but are not limited totetraisopropyltitanate, dibutyltin dilaurate and tetramethylguandine aswell as photoinitiators including those described herein above. Fillersor reinforcing materials, adhesion promoters, anti-oxidants, flameretardants and pigments, etc may also optionally be provided in themethod of the invention.

EXAMPLES Example 1 Preparation of methacryloxymethyltrimethoxysilaneInventive Capper

(Structural Formula VI)

A 500 ml three neck round bottom flask equipped with a mechanicalstirrer and condenser were charged with 21.6 g sodium methacrylate, 40ml dimethylformamide (DMF) and 0.04 grams of acrylate polymerizationinhibitor, hydroquinone (HQ) and 34.20 g ofchloromethyltrimethoxysilane. The mixture was heated under a closedsystem to 120° C. for 2.5 hours. After cooling to room temperature, themixture was vacuum filtered and the DMF distilled under vacuum at 40° C.-45° C. The crude reaction product was further vacuum fractionated toyield 24.54 g of the capper (56% yield). Capper VII was similarlyprepared using sodium acetate and chloromethyltrimethoxysilane.

Example 2 Preparation of Inventive Polymer A and C

Inventive polymer A was prepared by charging 1000 g of a 750 cps ofhydroxyl-terminated polydimethylsiloxane into a 2 liter three neck roundbottom flask and devolitizing the fluid under vacuum at 105° C. for onehour. The silanol was cooled to 75° C. and 40.29 g of capper (structuralformula VI) prepared according to Example 1 was added to the silanolalong with 1 ml of N-butyllithium in hexane (1.6 Molar). Endcappingoccurred immediately as evidenced by transformation of the clear silanolfluid into a cloudy mixture due to rapid boiling of the liberatedmethanol in silicone. The mixture was vacuum stripped with stirring at75° C. 20 g of Polymer A was then used to assess skin over time. PolymerC was similarly prepared, but using capper VII instead.

Example 3 Comparison of Inventive Polymer A with a Comparative Polymer B

Comparative polymer B is of identical composition to inventive polymer Aexcept that the comparative capped polymers contain a propyl rather amethyl linkage to the silicon. Methylacryloxypropyldimethoxysiloxy-terminated PDMS was used as comparative polymer B.Polymer C was prepared similarly as in Example 2 using methacryloxypropyl trimethoxy silane instead of methacryloxy methyl trimethoxysilane. Comparison of skin over times for inventive polymer A andcomparative polymer B after addition of catalyst(tetraisopropyltitanate, TIPT) are shown in Table 1. TIPT was preparedby mixing 0.1 g TIPT with 5 g of methyl-terminatedpoly(dimethylsiloxane) before its addition to the polymers.

TABLE 1 Skin over time (SOT) Polymer A Comparative Polymer B 0.1% TIPT40 min. >24 hours 0.2% TIPT 24 min. overnight 0.5% TIPT 12 min. 2.5-3hours

As is evident from Table 1, moisture curing using the reaction productof the composition of the invention results in a much faster cure incomparison to compositions prepared from a silane having a propenyllinkage rather than a methyl linkage linked to the silicon.

Example 4 Skin Over Time of Inventive Polymer A in the Presence ofCatalyst and Photoinitiator

23 g of inventive composition A was added to (MeN)₂C=NH in a closedvial. The skin over time was 3 minutes when 0.2% (tetramethylguanidine)TMG was added to the mixture. When 1% photoinitiator,diethylacetophenone (DEAP) was also added, the moisture cure slowed toabout 10 to 15 minutes. The formulation cured to silicone rubber whenirradiated with a medium pressure mercury lamp with an intensity of 70mW/cm² for 30 seconds.

Example 5 Skin Over Time for Inventive Polymer C: Comparison ofCatalysts and Photoinitiator

The effect of different catalysts on skin over time of the inventivecomposition C was compared as shown in Table 2. Inventive composition Cis an acetoxymethyltrimethoxysilane capped polydimethylsiloxane. The useof catalysts TIPT and TMG resulted in similar rates of skin over time.As shown in Table 2, the addition of photoinitiator, diethylacetophenone(DEAP) increased the rate of skin over time when used with the catalystTIPT. The effect on skin over time is not effected when DEAP is usedwith TMG.

TABLE 2 Composition C Curing agent Skin over time 0.1% TMG 5 min. 0.2%TMG 2 min. 0.1% TMG, 1% DEAP 5 min. 0.3% TIPT, 1% DEAP >10 min.

Examples 1-5 show that when the silane cappers used in the compositionshave a methyl rather than a propyl linkage to the silane, faster curingin the presence of a moisture catalyst occurred, as measured by skinover time. Additionally, endcapping of the silanol occurred immediatelyupon addition of lithium catalyst.

The examples also reveal that particular catalysts, such as TIPT, willincrease the curing time when used with the photoinitiator, DEAP. Thecatalyst, TMG, however, is not effected by DEAP and skin over time was 5minutes.

1. A curable composition comprising: a) a compound having the structuralformula:

wherein R is a C₁₋₂₀ alkyl which is optionally substituted or anunsaturated free radical-curing group; R¹ is hydrogen or a C₁₋₆hydrocarbon radical; R² is a hydrolyzable group; X is oxygen or

R³ is H or C₁₋₁₂ hydrocarbyl group; and b) a polymer having thestructural formula:

wherein A is a backbone selected from the group consisting of organicand siloxane backbones, and R^(e) is CH₃ or H, wherein formula I andformula II are present in amounts such that the resulting ratio of saidhydrolyzable groups of formula I to said OH groups of formula II is 1.2.2. The composition according to claim 1, wherein said curablecomposition is a dual cure photo/moisture curable composition.
 3. Themethod according to claim 2, wherein R is alkenyl, which may besubstituted or unsubstituted.
 4. The composition according to claim 1,wherein said curable composition is a moisture curable composition. 5.The method according to claim 4, wherein R is a C₁₋₂₀ alkyl which isoptionally substituted.
 6. The method according to claim 4, wherein R isa methyl group.
 7. The composition according to claim 1, wherein X is O.8. The composition according to claim 1, wherein R² is an alkoxy grouphaving the formula R⁴O- wherein R⁴ is a C₁₋₂ alkyl group.
 9. Thecomposition according to claim 1 wherein R is

and R⁵, R⁶ and R⁷ are independently selected from the group consistingof hydrogen, halogen and organo radicals.
 10. The composition accordingto claim 1 wherein A is a polysiloxane.
 11. A composition comprising (a)a compound having the structural formula

 wherein R is CH₃, R¹ is hydrogen or a C₁₋₆ hydrocarbyl group, R² isOR⁴, R⁴ is a C₁₋₂ alkyl group, and X is O, and (b) a polymer having thestructural formula

 wherein A is a backbone selected from the group consisting of organicand siloxane backbones, and R^(e) is CH₃ or H.
 12. The curablecomposition of claim 11 or claim 1 wherein said reaction product has askin over time when exposed to curingly effective conditions of 15minutes or less.
 13. The curable composition of claim 12 wherein saidreaction product has a skin over time when exposed to curingly effectiveconditions of 5 minutes or less.